1. Field of the Invention
The present invention relates to dielectric devices of a wide range of devices such as resonators, oscillators, dielectric filters, duplexers and the like.
2. Description of the Related Art
Such dielectric devices are used in a high-frequency range such as sub-microwave band, microwave band, millimeter wave band, or sub-millimeter wave band. More specific examples of applications include satellite communication devices, mobile communication devices, wireless communication devices, high-frequency communication devices, or base stations for such communication devices.
In conventional dielectric devices of this type, for example, in a dielectric filter as a representative example thereof, a plurality of resonator units are composed using a common ceramic dielectric body, those resonator units are interstage capacitively or inductively coupled, and a prescribed frequency component is extracted. The ceramic dielectric body is used commonly in a plurality of resonator units and most of the outer surface thereof, excluding the open end surface, is coated with a conductive film.
Each of the resonator units comprises a first hole passing therethrough to an opposite surface (short circuit surface) which is opposite to the open end surface. The height of the ceramic dielectric body from the open end surface to the short circuit surface is typically selected as (xcex/4), where xcex is a selected central frequency wavelength. Therefore, the first hole also has a length of about (xcex/4).
However, heavy demands are placed upon the decrease in thickness, size, and weight of satellite communication devices, mobile communication devices, wireless communication devices, and high-frequency communication devices using such dielectric devices, and this demand cannot be met by the conventional technology setting (xcex/4) as a standard for the height of the ceramic dielectric body from the open end surface to the short circuit surface.
Japanese Patent Publication No. 32321/1992 is known as a reference relating to prior art aimed at miniaturization of dielectric filters. The dielectric filter described in this publicly known reference can be conceptually considered as a dielectric filter obtained by cutting a ceramic dielectric body having a height of about (xcex/4) in a position of (xcex/8), which is half of (xcex/4), arranging the obtained two halves in a row so that the cut surfaces thereof tie at the same side, and then connecting the through conductors divided in two on the cut surfaces.
However, a problem associated with such conventional technology is that the through conductors determining the resonant wavelength matched the height of the ceramic dielectric body and the dimensions thereof were fixed which made it difficult to adjust the resonant frequency.
Furthermore, the open end surface and short circuit surface turn up in a relationship such that each of them takes a half of surface area on the surface opposite to the cut surface. As a result, the external connection structure of input and output terminals was difficult to conform to actual demands.
Thus, in the dielectric filters of this type, because of the demand placed upon miniaturization and decrease in thickness, it was necessary to employ an input and output terminal structure allowing for surface mounting on a circuit substrate.
However, since in the above-described conventional technology, the open end surface and short circuit surface turn up in a relationship such that each of them takes a half of the surface area on the surface opposite to the cut surface, a structure has to be employed in which the surface where the open end surface and short circuit surface are present is directed upward and a lead wire is connected to the through conductor appearing on the open end surface, which makes it difficult to employ a surface mounted structure.
An object of the present invention is to provide a dielectric device permitting miniaturization and decrease in thickness.
Another object of the present invention is to provide a dielectric device allowing for resonant frequency adjustment.
Still another object of the present invention is to provide a dielectric device suitable for surface mounting.
In order to attain the above-described objects, the dielectric device in accordance with the present invention comprises a dielectric substrate and at least one resonator unit. The dielectric substrate comprises an outer surface covered with an external conductor film, excluding at least one end surface.
The resonator unit comprises a first hole and a second hole. The first hole is provided in the dielectric substrate, directed from the end surface to the surface opposite thereto, and open at the end surface and opposite surface. Thus, the first hole is a through hole. A first internal conductor is provided inside the first hole.
The second hole is provided in the dielectric substrate so that it is spaced apart from the first hole, directed from the end surface toward the surface opposite thereto, open at said end surface, and closed at a bottom portion thereof. Thus, the second hole is a blind hole. A second internal conductor is provided inside the second hole. The second internal conductor is connected to the first internal conductor at the end surface.
As described above, in the dielectric device in accordance with the present invention, the resonator unit comprises the first hole and the second hole, the first hole comprises the first internal conductor, is directed from the end surface of dielectric substrate toward the surface opposite thereto, and is open at the end surface and opposite surface. Furthermore, the second hole is spaced apart from the first hole and is directed from the end surface toward the surface opposite thereto. The second hole is provided with the second internal conductor and the second internal conductor is connected to the first internal conductor at the end surface.
Therefore, in the dielectric device in accordance with the present invention, the resonator length defining the resonant wavelength is a sum (H1+H2+D1) of the length H1 of the through conductor corresponding to the height from the end surface of the dielectric substrate to the surface opposite thereto, the depth (height) H2 of the second hole directed from the end surface toward the surface opposite thereto, and the distance D1 from the second hole to the first hole. This means that when a prescribed resonant wavelength is obtained, the height from the end surface of the dielectric substrate to the surface opposite thereto can be decreased by the sum (H2+D1) of the depth of the second hole directed from the end surface toward the surface opposite thereto and the distance D1 from the second hole to the first hole, and the dimensions and thickness of the dielectric substrate can be decreased.
More specifically, when the resonant wavelength is (xcex/4), if the sum (H2+D1)=(xcex/8), the height H1 from the end surface of the dielectric substrate to the surface opposite thereto also becomes (xcex/8) and this height can be reduced from the usually required (xcex/4) to (xcex/8).
Moreover, the second hole is closed rather than open at the opposite surface, and a dielectric material having a thickness equal to a difference (H1xe2x88x92H2) between the height H1 of the dielectric substrate and the depth H2 of the second hole is present between the second hole and the opposite surface. Therefore, the depth H2 of the second hole can be adjusted and thus the resonant frequency can be adjusted by controlling the thickness of the dielectric material.
Furthermore, since the second hole is disposed at a distance D1 from the first hole, the resonant frequency can be also adjusted by setting the distance D1.
Moreover, the second hole is directed from the end surface toward the surface opposite thereto, is open at the end surface and is closed rather than open at the surface opposite to the end surface. Therefore, a terminal for surface mounting can be provided so as to be electrically insulated from the external conductor film in an appropriate position, for example, on a side surface or the surface opposite to the end surface. With such a structure, the terminal can be mounted onto the mounting substrate. A coupling capacitance is generated between the terminal and the internal conductor of the second hole, this capacitance being defined by the thickness and dielectric constant of the dielectric material therebetween and opposing surface areas thereof. The terminal can be also provided on the side surface of the dielectric substrate to create capacitive coupling with the internal conductor of the first hole.
In case of resonant wavelength (xcex/4), the surface opposite to the end surface serves as a surface (short circuit surface) covered with an external conductor film, but in case of resonant wavelength (xcex/2), the opposite surface serves as the end surface not covered with an external conductor film.
The dielectric device in accordance with the present invention covers a wide range of devices including resonators, oscillators, dielectric filters, duplexers (also referred to as antenna duplexers). When it is used as a resonator or oscillator, among those applications, one resonator unit may be sufficient. In dielectric filter or duplexer applications, there are a plurality of resonator units.
When the device in accordance with the present invention is used as a dielectric filter, a first terminal and a second terminal are provided and they are employed as input and output terminals. The first terminal is provided in a position opposite, via the dielectric substrate, to the second hole provided in one of the resonator units. The second terminal is provided in a position opposite, via the dielectric substrate, to the second hole provided in another resonator unit. Both those first and second terminals are insulated from the external conductor.
With such configuration, the first and second terminals can be surface mounted onto a mounting substrate. The first and second terminals may be provided on the opposite surface or they may be provided on the side surface of the dielectric substrate, excluding the end surface and opposite surface. Furthermore, the first and second terminals may be also provided so as to be capacitively coupled to the first internal conductor.
In case of application as a duplexer (antenna duplexer), at least three resonator units and first to third terminals are provided. The first to third terminals are installed according to respective different resonator units and are used as an antenna terminal, receive terminal, and transmit terminal.
With such configuration, the first to third terminals can be surface mounted onto a mounting substrate. The first to third terminals may be provided on the opposite surface or they may be provided on the side surface of the dielectric substrate, excluding the end surface and opposite surface. Furthermore, the resonant frequency can be adjusted by setting the depth of the second hole or the distance between the first hole and second hole.
Other objects, configurations, and advantages of the present invention will be described with greater detail hereinbelow with reference to the drawings attached. However, the technological scope of the present invention is obviously not limited to the embodiments thereof illustrated in the drawings.